Problem: If $a + b = -4$ and $x + y + z = 9$, what is $-5z - 10a - 10b - 5y - 5x$ ?
Solution: $= -10a - 10b - 5x - 5y - 5z$ $= (-10) \cdot (a + b) + (-5) \cdot (x + y + z)$ $= (-10) \cdot (-4) + (-5) \cdot (9)$ $= 40 - 45$ $= -5$